This invention is in the area of the manufacture of MEMS (microelectromechanical systems) as well as semiconductor devices, or any other devices that require removal of a material relative to a substrate or other deposited material. In particular, this invention addresses gas-phase etching procedures, with particular emphasis on etching rate with a preferably spontaneous chemical etchant as well as detection of the end point in an etching process. The invention is also directed to apparatus useful for etching and detecting the end point of the etching reaction. “MEMS”, “microelectromechanical” and “micromechanical” are used interchangeably throughout this application and each may or may not have an electrical component in addition to the microstructure component. The end point detected can be a point in an etch process where all of the material that is capable of reacting with the etchant gas has been removed and there is no more of the material remaining on the substrate or exposed to the etchant gas.
The use of etchants for removing sacrificial layers or regions in a multilayer structure without removal of an adjacent layer or region is a necessary and common step in the manufacture of semiconductor and MEMS devices. The MEMS devices of the present invention can be devices for inertial measurement, pressure sensing, thermal measurement, micro-fluidics, optics, and radio-frequency communications, with specific examples including optical switches, micromirror arrays for projection displays, accelerometers, variable capacitors and DC or RF switches. If a semiconductor device is etched, it can be any device that is made of or has on a substrate a material that is to be removed with a preferably gas phase chemical etchant.
The success of an etch step in the manufacture of microstructures is improved not only due to the selectivity of the etchant, but also due to the ability to accurately determine the end point of the etching process. Isotropic etching is of particular interest in processes where the purpose of the etch is to remove a sacrificial layer that is intervening between functional layers or between a functional layer and a substrate. Gas phase etchants, particularly in the absence of plasma, are desirable for isotropically removing a sacrificial layer.
Of potential relevance to certain embodiments of this invention is the prior art relating to particular etchant gases. Prominent among the etchants that are used for the removal of sacrificial layers or regions in both isotropic and anisotropic etching procedures are noble gas fluorides and halogen fluorides. These materials, used in the gas phase, selectively etch silicon relative to other materials such as silicon-containing compounds, non-silicon elements, and compounds of non-silicon elements. Descriptions of how these materials are used in etching procedures appear in co-pending U.S. patent application Ser. Nos. 09/427,841 and 09/649,569 to Patel et al. and in portions of the present specification that follow.
The method of the present invention is useful for achieving high selectivity and/or detecting an end point in methods for producing semiconductor devices and deflectable MEMS elements (deflectable by electrostatic or other means) which, if coated (before or after gas phase processing) with a reflective layer, can act as an actuatable micromirror. Arrays of such micromirrors can be provided for direct view or projection display systems (e.g. projection television or computer monitors), as well as for optical switching. The present invention is also adaptable to detecting an end point in methods for etching microfabricated devices other than deflectable MEMS devices (e.g. semiconductor based devices, carbon nanotubes on glass, nondeflectable MEMS devices such as sensors, etc.)